It supports thunderbolt and USB using a USB C connection and is also expandable via ADAT. I can get a great condition used one for around 200 GBP and was considering it as an upgrade to my existing audio interface (see signature).

Does anyone have any idea whether this would work reliably and provide very low latency? I know that PC based thunderbolt solutions can be a bit of a compatibility lottery but would this solution be any better compatibility wise?

The Clarett USB series has a USB-C port, but I want to clarify a couple things.

The Clarett USB audio interfaces do not support Thunderbolt.Look at the USB-C connection. Note that the logo is USB (not Thunderbolt).Also, the Clarett USB series connect via USB-C, but... they are USB-2 audio interfaces.

Regarding round-trip latency, they'll do about as well as an RME USB-2 audio interface.Slightly lower than 5ms total round-trip latency at a 64-sample ASIO buffer size (44.1k).

When it comes to round-trip latency, the best USB-3 audio interfaces are about equal to the best USB-2 audio interfaces.

If you want to achieve sub 3ms total round-trip latency, you have to go either PCIe or Thunderbolt.ie: The Presonus Quantum yields 1ms total round-trip latency at 96k (32-sample ASIO buffer size). As long as your machine can sustain the load, audio is completely glitch-free.

I also found this review today comparing various USB interfaces latency in Windows 10 including the 2Pre USB which didn't come out of it all that well in terms of latency. It was carried out in April 2018 (the 2nd not the 1st so hopefully not an April fool gag!) so I guess that Focusrite could have improved things slightly with driver updates but the Fireface UFX 1st gen was the clear winner.

With regard to Thunderbolt interfaces on a PC is it still the case that you need to pair a specific motherboard that supports it with a matched interface?

The motherboard has to have a Thunderbolt-3 header... and the BIOS has to specifically support the Thunderbolt-3 add-in-card.

Most Thunderbolt audio interfaces are Thunderbolt-2, so you'll need a Thunderbolt-3 to Thunderbolt-2 adapter (Apple and StarTech make them). Some audio interface manufacturers recommend the StarTech adapter. I'm not much of an Apple guy, but the Apple adapter has worked well in every situation we've tested (many different custom desktops/laptops).